1. Field of the Invention
The present invention relates to a method for manufacturing an electro-optical device having a light transmissive substrate and a monocrystalline layer bonded to the substrate, the electro-optical device and electronic equipment. In particular, the present invention relates to a method for manufacturing an electro-optical device having a light shielding layer formed on a light transmissive substrate, the electro-optical device and electronic equipment.
2. Description of the Related Art
The SOI technology in which a seminconductor device is formed on a silicon thin film on top of an insulating substrate is appropriate for use in an electro-optical device such as a liquid-crystal display device, because the SOI technology offers high-speed, low-power consumption features and the high degree of integration in devices.
When the SOI technology is applied to the electro-optical device, a monocrystalline silicon substrate is bonded to a light transmissive substrate, and is polished to form a thin monocrystalline silicon layer. Then, a transistor element such as a MOSFET for driving a liquid crystal is formed from the monocrystalline silicon layer.
In a projection-type display apparatus such as a projector employing a liquid-crystal display device, light is typically incident on the surface of a light transmissive substrate. The projection-type display apparatus is thus typically provided with a light shielding layer on a MOSFET to prevent a leakage photocurrent from entering a channel region of the MOSFET formed on the substrate.
Even if the light shielding layer is arranged on top of the MOSFET, light incident on the front surface is reflected from the back surface of the substrate, returns to and enters the channel region of the MOSFET, when a support substrate is light transmissive. Although the returning light is a mere fraction of the light quantity of light incident on the surface of the substrate, it is strong enough to cause a leakage photocurrent in an apparatus, such as a projector, which handles a high-power light source. The returning light from the back surface adversely affects the switching characteristics of the element, thereby degrading the device characteristics. Here, the surface having the monocrystalline silicon layer formed thereon is referred to as the front surface of the substrate, and the opposite surface thereof is referred as the back surface.
Japanese Unexamined Patent Application Publication No. 10-293320 discloses a technique for forming a light shielding layer on the surface of a substrate in an area corresponding to a transistor element. In such a technique, the light shielding layer is patterned on the surface of the substrate, an insulating layer is deposited on the light shielding layer and is then planarized, and a monocrystalline silicon substrate is then bonded onto the planarized surface.
Since such a liquid-crystal display device includes, on the substrate thereof, an area where transistor elements are concentrated and an area where no transistor elements are present, the light shielding layers are accordingly distributed on the substrate. Similarly, protrusions of the insulating layer prior to a polishing process are densely distributed in one area while sparsely distributed in the other area on the substrate. In the polishing process for planarizing the insulating layer, variations take place in polishing performance between the area of densely distributed protrusions and the area of sparsely distributed protrusions. Specifically, the thickness of the insulating layer becomes thick in the area of the densely distributed protrusions, while the thickness of the insulating layer becomes thin in the area of the sparsely distributed protrusions. As a result, the insulating layer suffers from waviness in the surface thereof subsequent to the polishing process.
If the insulating layer suffers from the waviness on the surface thereof, the following problems arise. First, a void is caused in the interface with the insulating layer and the monocrystalline silicon layer, and the MOSFET formed in the void suffers from poor performance characteristics or suffers from a complete failure. Second, the bond between the insulating layer and the monocrystalline silicon layer is weakened. A weakened bond in the MOSFET forming process subsequent to the formation of the monocrystalline silicon layer, causes a failure such as a peel of the monocrystalline silicon layer thereby decreasing the production yield of the device.
To resolve the above problems, the present invention has been developed. It is an object of the present invention to provide a method for manufacturing an electro-optical device that planarizes an insulating layer to which a monocrystalline silicon layer is bonded, the electro-optical device and electronic equipment.
To achieve the above object, a method for manufacturing an electro-optical device of the present invention includes the step of forming a light shielding layer on one side of a light transmissive substrate, patterning the light shielding layer, forming an insulating layer on the patterned light shielding layer, planarizing the insulating layer, bonding a monocrystalline silicon layer on the surface of the planarized insulating layer, and forming a transistor element from the monocrystalline silicon layer, wherein the patterned light shielding layer is arranged in an area facing the transistor element and in a peripheral area surrounding the transistor element.
In accordance with the manufacturing method of the present invention, the light shielding layer formed on one side of the light transmissive substrate is present not in either the formation area of the transistor element or in the peripheral area of the transistor element, and variations of protrusions of the substrate due to the light shielding layer are reduced. A uniformity in the polishing rate on the substrate is substantially improved when the insulating layer on the light shielding layer is planarized through the polishing process. Through the planarizing process of the insulating layer, the surface of the light transmissive substrate is thus planarized to be flat without introducing waviness therein. No void occurs in the interface between the insulating layer and the monocrystalline silicon layer, the bond between the insulating layer and the monocrystalline silicon layer increases, and the transistor element is thus free from variations in performance characteristics and failures.
In accordance with the present invention, the light transmissive substrate is bonded to a counter substrate by a sealing member, and the peripheral area area facing the sealing member. Since the light shielding layer is arranged facing the sealing member, the peripheral area is uniformly planarized, and the monocrystalline silicon layer is well bonded.
In the method of the present invention for manufacturing an electro-optical device, the step of planarizing the insulating layer formed on the light transmissive substrate uses a chemical mechanical polishing process.
An electro-optical device of the present invention includes a patterned light shielding layer formed on one side of a light transmissive substrate, a planarized insulating layer formed on the patterned light shielding layer, and a switching element formed on the planarized insulating layer, wherein the patterned light shielding layer is arranged in an area facing the transistor element and in a peripheral area surrounding the transistor element.
In accordance with the present invention, the surface of the insulating layer is thus planarized to be flat. No void occurs in the interface between the insulating layer and the monocrystalline silicon layer. An electro-optical device features a strong bond between the insulating layer and the monocrystalline silicon layer, with the transistor element free from variations in the performance characteristics and failures.
In the electro-optical device of the present invention, the pattern of the light shielding layer in an area having no transistor element therewithin extends in a pattern that is developed by two-dimensionally periodically repeating a pattern formed in an area where a transistor element is arranged.
Since the protruded state of the surface of the insulating layer in the area where no transistor elements are formed is similar to the protruded state of the transistor formation area before planarization in this arrangement of the present invention, uniformity in the polishing rate is improved, and surface waviness is reduced prior to the planarizing process. No void occurs in the interface between the insulating layer and the monocrystalline silicon layer. An electro-optical device features a strong bond between the insulating layer and the monocrystalline layer with the transistor element free from variations in the characteristics and failures.
In the electro-optical device of the present invention, the light transmissive substrate is fabricated of quartz, and the light shielding layer is fabricated of a refractory metal or a refractory metal-silicide. In the transistor formation process on the light shielding layer, a heat treatment above 1000xc2x0 C. can be performed to improve the device performance characteristics.
A method for manufacturing an electro-optical device of the present invention including a display area including on a transparent substrate a matrix of pixel electrodes and transistors connected to the respective pixel electrodes, an external-circuit interconnect terminal for receiving a signal from a drive circuit, an external-circuit arranged in a peripheral area surrounding the display area, including the steps of forming a light shielding layer on the transparent substrate, patterning the light shielding layer, forming an insulating layer on the patterned light shielding layer, planarizing the insulating layer, bonding a monocrystalline silicon layer on the surface of the planarized insulating layer, and forming a transistor element from the monocrygtalline silicon layer, wherein the patterned light shielding layer is arranged in an area of the transistor element and in an area peripheral thereto, and the light shielding layer in the peripheral area is arranged to face the drive circuit.
In accordance with the manufacturing method of the present invention, the pattern of the light shielding layer is present both in the formation area of the transistor element and in the peripheral area of the transistor element, and variations in the distribution of protrusions of the substrate due to the light shielding layer are small. A uniformity in the polishing rate on the substrate is substantially improved when the insulating layer on the light shielding layer is planarized through the polishing process. Since the peripheral area is easy to polish during the planarizing process, arranging the light shielding layer in the peripheral area reduces the variations in the distribution of protrusions in the substrate. No void occurs in the interface between the insulating layer and the monocrystalline silicon layer, the bond between the insulating layer and the monocrystalline silicon layer is increased, and the transistor element is thus free from variations in the performance characteristics and failures. Additionally, by arranging the light shielding layer in the area facing the drive circuit, no light is permitted to enter the drive circuit, and the transistor formed in the drive circuit is free from erratic operations.
In the method for manufacturing an electro-optical device of the present invention, the patterned light shielding layer is arranged in an area facing the external-circuit interconnect terminal.
In accordance with the manufacturing method of the present invention, the waviness is controlled through the planarizing process of the insulating layer, because the light shielding layer is arranged in the area facing the external-circuit interconnect terminal.
A method for manufacturing an electro-optical device of the present invention including a display area, includes a transparent substrate a matrix of pixel electrodes and transistors connected to the respective pixel electrodes, an external-circuit interconnect terminal for receiving a signal from a drive circuit, an external-circuit arranged in a peripheral area surrounding the display area, including the steps of forming a light shielding layer on the transparent substrate, patterning the light shielding layer, forming an insulating layer on the patterned light shielding layer, planarizing the insulating layer, bonding a monocrystalline silicon layer on the surface of the planarized insulating layer, and forming a transistor element from the monocrystalline silicon layer, wherein the patterned light shielding layer is arranged in an area of the transistor element and in an area peripheral thereto, and the light shielding layer in the peripheral area is arranged in the vicinity of the drive circuit and the external-circuit interconnect terminal but not arranged in an area facing the drive circuit.
Since the light shielding layer in accordance with the manufacturing method of the present invention, is formed in the peripheral area surrounding the drive circuit and the external-circuit interconnect terminal variations in the distribution of the protrusions of the insulating layer thereon are reduced. Since no light shielding layer is arranged in the area facing the drive circuit and the external-circuit interconnect terminal, the electrical effect caused by the light shielding layer is limited.
In accordance with the method for manufacturing an electro-optical device of the present invention, the step of planarizing the insulating layer uses a chemical mechanical polishing process.
In accordance with the manufacturing method of the present invention, the light shielding layer is formed in the display area and the peripheral area, and the insulating layer is deposited on the light shielding layer. The peripheral area is planarized with less waviness involved.
In accordance with the method for manufacturing an electro-optical device of the present invention, the light shielding layer arranged in an area facing the transistor and the light shielding layer arranged in an area facing the drive circuit have generally identical shapes.
Since the light shielding layer arranged in the area facing the transistor and the light shielding layer arranged in the area facing the drive circuit have generally identical shapes in accordance with the manufacturing method of the present invention, the spacings between the light shielding layers become substantially uniform, and the degree of waviness is further reduced through the planarizing process of the insulating layer thereon.
An electro-optical device of the present invention further includes the other light transmissive substrate which is arranged opposite from the surface of the light transmissive substrate having the monocrystalline silicon layer thereon, a liquid crystal interposed between the two light transmissive substrates, and driven by a transistor element formed within the transistor.
Electronic equipment of the present invention includes a light source, an electro-optical device described above, for modulating a light beam entering thereon from the light source in response to image information, and projection means for projecting modulated light beam from the electro-optical device.